Method for producing isopentene

ABSTRACT

Isopentene is produced in a high yield by the method wherein a hydrocarbon mixture containing isobutene and n-butene is brought into contact with a catalyst which has been prepared by depositing a molybdenum compound and at least one additional metal compound such as cobalt, tin, silver, zinc, cadmium, lead, bismuth or antimony compound, on an alumina carrier and calcining the compounds, deposited thereon, the contact being carried out in the presence of steam in an amount of 0.1 to 25% based on the volume of the hydrocarbon mixture and calculated in terms of volume under standard conditions of 0*C and 760 mmHg in order to disproportionate the hydrocarbon mixture, and the resultant isopentene is isolated from the reaction mixture.

States Patent 1 Nakatomi et a1.

[ 1 Mar. 18, 1975 METHOD FOR PRODUCING ISOPENTENE [73] Assignee: UBE Industries, Ltd., Ube-shi,

Yamaguchi-ken, Japan [22] Filed: June 6, 1974 [21] Appl. No.: 476,938

[30] Foreign Application Priority Data June 22, 1973 Japan 48-69802 [52] US. Cl 260/683 D, 252/465, 260/683.15 R [51] Int. Cl. C07c 3/62 [58] Field of Search 260/683 D 56] References Cited UNITED STATES PATENTS 3,261,879 7/1966 Banks 260/683 3,544,648 12/1970 Wilson.... 260/683 3,546,314 12/1970 Larson 260/683 3,637,891 1/1972 McGrath et a1. 260/683 3,658,929 4/1972 Banks 260/683 3,668,270 6/1972 Martin et a1. 260/683 3,697,613 10/1972 Arganbright 4. 260/683 3,808,285 4/1974 Hughes 260/683 Primary Examiner-Delbert E. Gantz Assistant Examiner-C. E. Spresser [57] ABSTRACT Isopentene is produced in a high yield by the method wherein a hydrocarbon mixture containing isobutene and n-butene is brought into contact with a catalyst which has been prepared by depositing a molybdenum compound and at least one additional metal compound such as cobalt, tin, silver, zinc, cadmium, lead. bismuth or antimony compound, on an alumina carrier and calcining the compounds, deposited thereon, the contact being carried out in the presence of steam in an amount of 0.1 to 25% based on the volume of the hydrocarbon mixture and calculated in terms of volume under standard conditions of 0C and 760 mmHg in order to disproportionate the hydrocarbon mixture, and the resultant isopentene is isolated from the reaction mixture.

22 Claims, No Drawings 1 METHOD FOR PRODUCING ISOPENTENE The present invention relates to a method for producing isopentene, more particularly, relates to a method for producing isopentene by disproportionation of a hydrocarbon mixture containing isobutene and nbutene.

The term isopentene used herein refers to 2- methylbutene-l, 2-methylbutene-2, 3-methylbutene-1 or mixtures of two or more of the above-mentioned compounds.

The term n-butene" used herein refers to cisbutene-Z, trans-butene-Z, butene-l or mixtures of two or more of the above-mentioned butenes.

It is known that olefins may be disproportionated by bringing them into contact with a molybdena-alumina catalyst. However, it is also known that if the conventional disproportionation method using the molybdenaalumina catalyst is applied to olefin mixtures containing mainly hydrocarbons having four carbon atoms, such as isobutene and n-butene, this application involves the following disadvantages.

1. Low disproportionation conversion The term disproportionation conversion used herein refers-to the ratio in percent of the weight of the disproportionation product to the original weight of the hydrocarbon mixture subjected to the disproportionation process.

2. Low content of C fraction in the resultant disproportionation product The term C fraction used herein refers to a fraction of distillate consisting essentially of hydrocarbons having five carbon atoms, separated from the disproportionation product.

3. High content of C fraction in the disproportionation product The term C fraction used herein refers to a fraction of distillate consisting essentially of hydrocarbons having six or more carbon atoms, separated from the disproportionation product.

4. Low content of isopentene in the C fraction Accordingly, it is known that the conventional method as stated above has a low industrial value for producing isopentene by the disproportionation process. This will become apparent by reading Reference Example 1 illustrated hereinafter.

Further, in the conventional disproportionation of olefin using a conventional catalyst, for example, molybdena-alumina catalyst, it is known that supplying steam to the disproportionation reaction system causes a remarkable decrease of the disproportionation conversion. This will become apparent by reading Reference Example 2 described hereinafter.

An object of the present invention is to provide a method for producing a high yield of isopentene by disproportionation of a hydrocarbon mixture containing isobutene and n-butene such that the hydrocarbon mixture can be disproportionated in a high conversion, the resultant disproportionation product contains a high content of C fraction and the C fraction contains a very high content of isopentene.

The above object can be accomplished by the method of the present invention which comprises the steps of bringing a hydrocarbon mixture containing isobutene and n-butene into contact with a catalyst which has been prepared by depositing a molybdenum compound and at least one additional metal compouond selected from the group consisting of cobalt, tin, silver, zinc, cadmium, lead, bismuth and antimony compounds on an alumina carrier and calcining the compounds deposited thereon, the contact being carried out in the presence of steam in an amount of0.l to 25% based on the volume of said hydrocarbon mixture and calculated in terms of volume under standard conditions of a temperature of 0C and a pressure of 760 mmHg, at a temperature of 220 to 380C, and isolating the resultant isopentene from the reaction mixture.

In the method of the present invention, the disproportionation product consists of a relatively high content of propylene, a relatively high content of C fraction and a relatively low content of C fraction which fractions consist of olefin compounds. That is, the disproportionation product obtained by the method of the present invention contains a high content of propylene and the C fraction both of which are very valuable to the chemical industry.

The disproportionation step in the method of the present invention may result in dimerization and isomerization of a minor portion of the hydrocarbon mixture while the major portion of the hydrocarbon mixture is disproportionated.

The catalysts usable for the method ofthe present invention are prepared by depositing a molybdenum compound and at least one additional metal compound selected from the group consisting of cobalt, tin, silver, Zinc, cadmium, lead, bismuth and antimony compounds on an alumina carrier and calcining the compounds deposited on the alumina carrier.

The additional metal compounds may be halides, sulfates, nitrates, carbonates, hydroxides, oxides, hydroxycarbonates and organic acid salts of cobalt, tin, silver, zinc, cadmium, lead, bismuth and antimony. The cobalt compound may be cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt formate, cobalt oxalate, cobalt hydroxide, cobalt carbonate or cobalt oxide.

The tin compound may be tin (II) chloride (stannous chloride), tin (ll) bromide, tin (ll) oxide, tin (II) nitrate or tin (II) acetate.

The silver compound usable for the catalyst may be silver chloride, silver bromide, silver nitrate, silver carbonate, silver oxalate, silver oxide or silverhydroxide.

The zinc compound usable for the catalyst may be zinc chloride, zinc bromide, zinc sulfate, zinc nitrate, zinc carbonate, zinc oxalate, zinc acetate or zinc oxide.

The cadmium compound usable for the catalyst may be cadmium chloride, cadmium nitrate, cadmium sulfate, cadmium carbonate, cadmium oxide, cadmium acetate or cadmium oxalate.

The lead compound usable for the catalyst may be lead chloride, lead nitrate, lead sulfate, lead carbonate, lead hydroxide, lead hydroxycarbonate, lead oxide, lead acetate or lead formate.

The bismuth compound usable for the catalyst may be bismuth chloride, bismuth nitrate, bismuth sulfate, bismuth hydroxycarbonate, bismuth oxide or bismuth oxalate.

The antimony compound usable for the catalyst may be antimony chloride, antimony sulfate, antimony hydroxide, or antimony oxide.

The molybdenum compound usable for the preparation of the catalyst for the method ofthe present invention may be selected from the molybdenum compounds usable for the ordinary catalyst for the conventional method, preferably, may be molybdenum oxide, ammonium molybdate, molybdenum chloride or molybdenum oxide chloride.

The alumina usable as a carrier for the preparation of the catalyst for the method of the present invention may be preferably selected from activated alumina, for example, 'y-alumina and n-alumina. Such alumina may have the usual configuration of the conventional catalysts.

Preferably, the alumina usable for the catalyst of the method of the present invention is fine particles of a 2 to 100 mesh size, more preferably, 4 to 50 mesh size.

The molybdenum compound and the additional metal compound as specified above may be deposited on the alumina carrier by conventional methods, for example, the co-precipitation method wherein all of the molybdenum compound, the additional metal compound and an aluminium compound are simultaneously precipitated from the solution thereof, or the impregnation method wherein the alumina is impregnated with a solution of both the compounds and is then dried.

in the impregnation method, the molybdenum compound and the additional metal compound may be deposited simultaneously on the alumina or separately deposited in any order. For example, the molybdenum compound is deposited on the alumina and calcined to remove water absorbed by the alumina, and thereafter, one or more of the additional metal compounds are deposited on the molybdenum compound-deposited alumina, and calcined to prepare the desired catalyst. Also, the additional metal compound may be deposited on a commercial molybdena-alumina catalyst. The molybdenum compound and the additional metal compound deposited on the alumina carrier are calcined at a temperature of 300 to 1000C, preferably, 500 to 700C for 3 to 10 hours in air flow or nitrogen flow, by a conventional calcining method, for example, using an electric furnace.

The catalyst usable for the method of the present invention preferably contains 5 to 20% of the calcined molybdenum compound and 0.5 to more preferably, l to 5%, of the additional metal compounds each based on the weight of the alumina and each calculated in terms of oxide corresponding to the compound.

The hydrocarbon mixture usable for the method of the present invention contains isobutene and n-butene. it is preferable that isobutene in the hydrocarbon mixture be in an amount of 30% or more, more preferably, 30 to 60% by weight. That is, the n-butene may contain butene-l. In the conventional method for butenes, it is known that an increase in the butene-l content in the hydrocarbon mixture causes an undesirable increase in the content of n-pentenes in the C fraction. However, in the disproportionation step of the method of the present invention, butene-l in the hydrocarbon mixture is isomerized to butene-2 and simultaneously disproportionated. Accordingly, in the method of the present invention, the undesirable production of n-pentene is very little. That is, the C fraction produced by the process of the present invention includes a very high content of isopentene; in other words, it consists essentially of isopentene.

The hydrocarbon mixture usable for the method of the present invention may contain, other than isobutene and n-butene, hydrocarbons such as n butane, isobutane, propylene, propane, l,3-butadiene, isopendisp roportionation tane, isopentene, isoprene, n-pentane and n-pentenes. It is preferable that the total content of the other hydrocarbons contained in the hydrocarbon mixture be not higher than 15% by weight. Especially, it is desirable for the content of conjugated diene compounds, for example, l,3-butadiene and isoprene, to be 1.0% by weight or less.

The hydrocarbon mixture usable for the method of the present invention may be a so-called spent BB fraction which is an extraction residue prepared by extracting l,3-butadiene from a fraction of distillate consisting of hydrocarbons having four carbon atoms (C, fraction) produced by thermal decomposition or catalytic cracking of natural gas, petroleum gas, naphtha or other petroleum fraction.

In the disproportionation step in the method of the present invention, there is no limitation in feed rate of the hydrocarbon mixture. However, it is preferable that the hydrocarbon mixture be brought into contact with the catalyst at a flow rate, per 1 cm of the catalyst, of 50 to 2,000 cm /hour, more preferably, to 1,000 cm /hour calculated in terms of volume under the standard conditions of a temperature of 0C and a pressure of 760 mmHg.

In the method of the present invention, steam is fed into the disproportionation process in an amount of 0.1 to 25%, preferably, 0.2 to 10.0% based on the volume of the hydrocarbon mixture to be disproportionated and calculated in terms of volume under standard conditions. If the feed ofsteam is less than 0.1% by volume, undesirable side reactions, such as dimerization of isobutylene, are enhanced. As a result of the enhancement of the undesirable side reactions, the content of C, fraction in the disproportionation product undesirably increases and the content of isopentene in the C fraction decreases. If the feed of steam is greater than 25% by volume, the disproportionation conversion ratio undesirably tends to be lowered.

The steam supply method for the disproportionation process may be optionally selected from conventional methods if the method can feed steam at a uniform and stable rate. For example, in one steam supply method, the hydrocarbon mixture flows through a water bath maintained at a predetermined temperature so that a quantity of water is vaporized and mixed with the hydrocarbon mixture at a constant rate. ln an another steam supply method, the hydrocarbon mixture is admixed with a predetermined amount of steam which has been preliminarily generated. in still another steam supply method, the hydrocarbon mixture flows along the surface of a water bath having a predetermined temperature so as to mix with steam vaporized from the water bath. The hydrocarbon mixture containing the predetermined amount of steam is brought into contact with the catalyst.

In still another steam supply method, the hydrocarbon mixture is introduced into an aqueous solution saturated with a metal salt which is effective to maintain the vapor pressure of the solution constant, for example, calcium chloride, potassium bromide, zinc sulfate and magnesium nitrate. The mixture is then brought into contact with the catalyst.

If it is necessary, the catalyst for the method of the present invention may be treated with an inert gas, for example, nitrogen gas, containing 0.1 to 25% by volume of steam calculated in terms of volume under standard conditions, at a temperature of 100 to 300C.

This treatment is effective for enhancing initial activity of the catalyst and its effect can be seen in Example 2, illustrated hereinafter.

In the method of the present invention, the disproportionation process is carried out at a temperature between 220 and 380C, preferably, between 230 and 350C. A disproportionation temperature of less than 220C results in a undesirably high content of C frac tion in the disproportionation product. Also, a disproportionation temperature of more than 380C causes a undesirably low ratio of the disproportionation conversion, shortened life of the catalyst and increased decomposition of the hydrocarbon mixture.

Accordingly, the temperatures less than 220C or more than 380C are unsuitable for the practical disratio was calculated as a ratio in percent of the weight proportionation process in the method of the present invention.

Disproportionation in the method of the present invention is preferably carried out under normal pressure or a pressurized condition up to 10 kg/cm G.

When the hydrocarbon mixture containing isobutene and n-butene is disproportionated by the method of the present invention, the resultant disproportionation product consists essentially of propylene, hydrocarbons having five carbon atoms (C fraction) and hydrocarbons having six or more carbon atoms (C fraction). Both the C fraction and C fraction consist of olefins. The content of the C fraction in the disproportionation product does not exceed 25% by weight. The C fraction contains an isopentene content of not less than 95%. Accordingly, the method of the present invention produces high yields of propylene and isopentene which are very useful to the chemical industry. Further, isopentene obtained by the method of the present invention can be readily isolated and purified by conventional methods. That is, the C fraction can be isolated from the reaction mixture by distillation at a temperature of to 40C under normal pressure. The C fraction thus isolated consists essentially ofisopentene and, therefore, can be subjected to an isoprene producing process wherein the isopentene is dehydrogenated.

The present invention will be further illustrated by the following examples which are given for purposes of illustration only and not as limitations to the scope of the present invention.

In the following examples, reference examples and comparison examples, composition of the disproportionation product was determined by the method detailed below. After the disproportionation process was completed, the reaction mixture was subjected to gas chromatography analysis to determine and record amounts of the component hydrocarbons in the reaction mixture. From the record of the gas chromatography analysis which contains the analysis results of all the component compounds in the reaction mixture, the analysis results of the disproportionation product hydrocarbons were isolated from the analysis results of the non-reacted hydrocarbons in the reaction mixture.

From said isolated analysis results, the contents of the component hydrocarbons in the disproportionation product were calculated in based on the weight of the disproportional product. Also, the contents of the C fraction and the C fraction were calculated from the result of the gas chromatography analysis in the same manner as stated above. Further, the content of isopentene was calculated on the basis of the weight of the C fraction. The disproportionation conversion of the disproportionation product to the original weight of the hydrocarbon mixture subjected to the disproportionation process.

REFERENCE EXAMPLE 1 Production of isopentene using a catalyst composed of a molybdenum compound deposited on an alumina carrier In order to prepare a catalyst, 'y-alumina having a 14 to 32 mesh size (ASTM) was impregnated with an aqueous solution of5% by weight ofammonium molybdate, dried and, then, calcined in air flow at a temperature of 400C for 4 hours. The resultant catalyst was composed of 92.5% by weight of alumina and 7.5% by weight of the calcined molybdenum compound calculated in terms of molybdenum oxide.

A spent BB fraction gas consisting of 48.7% by weight of isobutene, 16.4% by weight of butene-Z, 26.3% by weight of butene-l, 1.2% by weight of isobutane, 7.1% by weight of n-butane, and 0.3% by weight of the sum of propane, propylene, 1.3-butadiene and propadiene, was brought into contact with 6 cm ofthe above-prepared catalyst at a flow rate of 500 cm /cm .catalyst/hr at a temperature of 250C under normal pressure to effect the disproportionation of the spent BB fraction.

Table 1 indicates the disproportionation conversion ratio in the above process, content of the resultant isopentene in C fraction and composition of the disproportionation product, at the stages 1.5 and 2.5 hours after the start of the disproportionation process.

REFERENCE EXAMPLE 2 Production of isopentene in the presence of steam using the same catalyst as in Reference Example 1 The same operation as in Reference Example 1 were repeated except that the same spent BB fraction gas as used in Reference Example 1 was flowed through a water bath maintained at a temperature of 0C by cooling under normal pressure so that 0.6% by volume of water calculated in terms of volume under standard conditions, i.e., 0C and 760 mmHg, was mixed with the spent BB fraction gas.

Table 1 indicates the results of the above disproportionation process, disproportionation conversion. content of the resultant isopentene in C fraction and composition of the disproportionation product, at the stages of 1.5 and 2.5 hours after the start of the disproportionation process.

EXAMPLE 1 In order to prepare a catalyst, y-alumina having a 14 to 32 mesh size was impregnated with an aqueous solution of 5% by weight of ammonium molybdate, dried and calcined at a temperature of 400C for 4 hours in air flow. The material impregnated and calcined above was impregnated with an aqueous solution of 4.3% by weight of cobalt nitrate, dried and calcined at a temper ature of 600C for 4 hours in air flow. Thereafter, the resultant material was further impregnated with an aqueous solution of 0.7% by weight of tin (II) chloride, dried and, then, calcined at a temperature of 600C for 3.5 hours in air flow. The resultant catalyst was composed of 92.5 parts by weight of alumina, 1 part by weight of the calcined tin compound calculated in terms of tin oxide (SnO), 2 parts by weight of the calcined cobalt compound calculated in terms of cobalt oxide (C) and 7.5 parts by weight of the calcined molybdenum compound calculated in terms of molybdenum oxide (M00 The same spent BB fraction gas as used in Reference Example 1 was flowed through a water bath maintained at a temperature of 0C by cooling under normal pres-' sure so as to be mixed with 0.6% by volume of steam calculated in terms of volume under standard conditions, and brought into contact with 6 cm of the aboveprepared catalyst at a temperature of 250C under normal pressure in order to effect the disproportionation of the spent BB fraction. The fraction was fed at a flow rate of 500 cm' /cm catalystlhour calculated in terms of volume under standard conditions i.e. 0C and 760 mmHg. Table 2 indicates the results of the above disproportionation, that is, the disproportionation conversion content of isopentene in C fraction and composition of the resultant disproportionation product at the stages of 1.5, 2.5, 3.5 and 4.5 hours after the start of the disproportionation process.

Table 2 Dispro- Dispro- Content of Composition of portionportionisopentene disproportionation ation ation in C product (7:) convertime sion fraction Pro- C C (hr) ("/1) (71) pylene fraction fraction In comparing Table 2 with Table 1, it is obvious that theprocess of the present example is superior to that of Reference Examples 1 and 2 in the disproportionation conversion ratio, the content of C 5 fraction in the disproportionation product and the content of isopentene in the C fraction. Especially, it should be noted that in comparing the present example with Reference Example 2, the use of cobalt and tin compounds as the component of the catalyst is effective for enhancing the disproportionation conversion, the content of the C fraction in the disproportionation product and the content of isopentene in the C fraction.

COMPARISON EXAMPLE 1 The same operations as in Example 1 were repeated except that the spent BB fraction gas was brought directly into contact with the catalyst without it flowing through the water bath. The results are indicated in Note: The disproportionation product contained a small amount of etlulene.

From a comparison of Table 3 with Table 2, it is evident that the absence of steam in the disproportionation process results in decreases of the disproportionation conversion, the content of the C fraction in the disproportionation product and the content of isopentene in the C fraction.

EXAMPLES 2, 3, AND 4 AND COMPARISON EXAMPLE 2 In Example 2, the same operations as in Example 1 were repeated except that the same catalyst as in Example I was steam-treated by bringing a mixture gas of nitrogen and 0.6% of steam, based on the volume of the nitrogen and calculated in terms of a volume under standard conditions into contact with the catalyst at a flow rate of 1,000 cm /cm .catalyst/hr at a temperature of 250C for 30 minutes. The results are indicated in Table 4.

In Example 3, the same procedures as in Example 1 were repeated except that the disproportionation process was carried out at a temperature of 300C instead of 250C. The results are indicated in Table 4.

In Comparison example 2, the same procedures as in Example 1 were repeated except that the disproportionation temperature was 200C instead of 250C. The results are indicated in Table 4.

In Example 4, the same procedures as in Example 1 were repeated except that the feed rate of the same spent BB fraction gas as in Example 1 was 1,000 cm /cm .catalyst/hr calculated in term of volume under standard condition, i.e. 0C and 760 mmHg. The results are shown in Table 4.

Table 4 Feed rate of Dispropor- Dispropor- Dispropor- Content of Composition of material tionation tionation tionation isopentene disproportionation hydrocarbon temperature time conversion in C product (71) Example mixture fraction No. (cm lcm Pro- C; C

catalyst/hr) (C) (hr) pylene fraction fraction 0.5 23.l 100 29.8 54.1 |6.I Example 2 500 250 1.5 25.3 100 30.8 54.6 14.6 2.5 23.0 100 32.2 55.2 12.6 Example 3 500 300 1.5 [2.6 100 36.0 50.9 13.1 Comparison Example 2 500 200 1.5 12.1 100 18.7 39.2 41.9 Example 4 1000 250 3.5 14.2 100 30.7 54.8 14.5

EXAMPLES 5 THROUGH 10 In each of Examples 5 through 10, a catalyst of the composition as indicated in Table 5 was prepared using the same method as used in Example 1. The amount each of the calcined metal compounds in the catalysts was calculated in terms of a metal oxide corresponding to the metal compound. The same procedures as in Example l were repeated using the above-prepared cata lysts. The results of the disproportionation process in each of the examples at a stage of 3.5 hours after the start of the process, are indicated in Table 5.

prepared by the method wherein 'y-alumina having 14 5 to 32 mesh size was impregnated with an aqueous solution of ammonium molybdate, dried and calcined at av Table 5 Dispropor- Content of Composition of Composition of catalyst tionation isopentene disproportionation conversion in C product Example (parts by weight) fraction No. SnO CoO MoO A1 Propylene C fraction C fraction 5 0.8 3.5 86.5 19.3 100 31.6 53.3 l5.l 6 1.0 3.5 10 86.5 19.1 100 30.4 54.5 15.0 7 1.3 3.5 10 86.5 21.3 100 33.9 51.6 14.6 8 2.7 3.5 10 86.5 19.4 100 31.2 55.5 13.2 9 1.0 0 7.5 92.5 21.7 100 31.0 53.3 15.6 10 0 3.5 10 86.5 [7.9 100 30.6 46.1 22.2

COMPARISONEXAMPLE 3 i The same procedures as in Example 10 were repeated except thatthe spent BB fraction gas was di- 0 Example 11 were repeated except that the disproportionation process was carried out in the absence of steam. the results are summarized in Table 6.

Table 6 Dispropor- Content of Composition of Composition of tionation isopentene disproportionation Example catalyst conversion in product 0. (parts by weight) C fraction AgO M00 A1 0 Propylene C fraction C. fraction 11 l 7.5 92.5 22.6 100 30.6 45.9 23.9 12 2 7.5 92.5 21.6 100 31.6 54.3 14.1 13 4 7.5 92.5 23.1 100 31.2 55.6 [3.2 14 6 7.5 92.5 22.1 100 31.1 49.8 19.1 Comparison Example 4 l 7.5 92.5 11.9 82.4 27.5 40.2 32.3

rectly brought into contact with the catalyst without flowing through the cold water at a temperature of 0C. At a stage of 3.5 hours after the start of the disproportionation process, the disproportionation conversion ratio was 10.3%, the content of isopentene in C5 fraction 68.8%, and the disproportionation product contained 29.8% of propylene, 32.2% of C fraction, 34.3% of C fraction and 3.7% of ethylene.

EXAMPLES 11 THROUGH 14 AND COMPARISON EXAMPLE 4 In Examples 11 through 14, four types of catalysts having the compositions as indicated in Table 6 were EXAMPLES 15 AND 16 In Example 15. the same operations as in Example 12 were repeated except that the catalyst was prepared by using zinc nitrate instead of silver nitrate.

ln Example 16, the same operations as in Example 6 were carried out except that the catalyst was prepared by using zinc nitrate in place of tin (ll) chloride.

The results of both examples l and 16 are indicated in Table 7.

was prepared by the method wherein y-alumina of 14 to 32 mesh size was impregnated with an aqueous solu- Table 7 Dispropor- Dispropor- Content of Composition of tionation tionation isopentene disproportionation time conversion in C product fraction (73) Ex. Catalyst Pro- C C No. (hr) pylene fraction fraction 1.5 19.8 100 28.3 47.3 24.4 15 Zn-Mo-A1 O 2.5 v 25.5 99.8 34.3 52.4 13.3 16 Zn-Co-Mo-AhO COMPARISON EXAMPLE 5 The same operations as in Example 15 were carried out in the absence of steam. At a moment of 3.5 hours after the start of the disproportionation process, the disproportionation conversion was 11.4%, the content of isopentene in C fraction was 66.3% and the disproportionation product contained 24.4% of propylene, 42.0% of C fraction and 32.2% of C fraction.

EXAMPLES 17 THROUGH 19 The same procedures as in Example 1 were repeated three times except that the water bath through which the spent BB fraction gas flowed, had the temperatures as shown in Table 8 and after being flowed through the water bath, the spent BB fraction gas included steam in amounts as shown in Table 8. The results are summarized in Table 8.

20 tion of 5% by weight of ammonium molybdate. dried and calcined at a temperature of 400C for 4 hours in air flow. Thereafter, the alumina impregnated and calcined above was further impregnated with an aqueous solution of 0.8% by weight of cadmium chloride, dried and, then, calcined at a temperature of 600C for 3.5 hours in air flow. The resulting catalyst was composed of 1 part by weight of the calcined cadmium compound, 7.5 parts by weight of the calcined molybdenum compound and 92.5 parts by weight of alumina, each calculated in terms of oxide corresponding to the compound.

ln Example 20, the same procedures as in Example 1 were carried out using the above-prepared catalyst.

In Comparison Example 6, the same procedures as in Example 20 were carried out except that the spent BB fraction gas was brought directly into contact with the catalystwithout flowing it through the water bath and Table 8 Content of Content of Composition of Temperature steam in Dispropor- Disproporisopentene disproportionation Ex. of water material tionation tionation in C product (91) No. bath hydrocarbon time conversion fraction mixture Pro- C 5 C (C) by volume) (hr) (92) pylene fraction fraction EXAMPLE 20 AND COMPARISON EXAMPLE 6 55 the disproportionation was carried out in the absence of Steamln Example 20 andComparisonfixample 6 a catalyst The results are indicated in Table 9.

Table 9 Dispropor- Dispro or- Content of Composition of Example tionation tionation isopentene in disproportionation product No. time conversion C, fraction (1%) (hr) (96) (1%) Propylene C, fraction C. fraction 2.5 21.0 100 32.7 49.5 17.8 20 3.5 20.0 100 35.9 50.1 14.0 4.5 17.5 100 36.6 47.5 15.9 2.5 19.0 62.1 33.2 40.6 24.6 Comparison 3.5 16.1 60.9 30.2 42.7 25.9 Example 6 v 4.5 12.8 64.0 28.8 43.9 26.1

Note: The disproportionation product of Com parison Example 6 included a small amount of ethylene.

EXAMPLES 21 THROUGH 23 14 EXAMPLES 26 AND 27 The same operations as in Example were repeated twice except that the spent BB fraction gas was fed into 1 the water bath at flow rates of 300 cm/cm.catalyst/hr (Example 26) and 1,000 cm/cm".catalyst/hr (Example .2?) cal ul d n. t rmss ql uhw n Table 10 Dispropor- Dispropor- Content of Composition of Ex. Metal tionation tionation isopentene in disproportionation product No. Compound time conversion C fraction (1H (hr) Propylene C fraction C. fraction 1.5 12.2 100 28.6 50.9 20.5 21 Lead nitrate 2.5 10.8 100 30.5 51.3 18.2 3.5 10.8 100 31.0 52.0 17.0 22 Bismuth 1.5 18.4 96.1 31.8 43.7 24.5 trichloride 2.5 16.9 100 36.4 46.4 17.2 V 3.5 15.7 100 35.4 48.1 16.5 23 Antimony 1.5 16.0 100 29.1 44.8 26.1 trichloride 2.5 13.8 100 29.9 49.0 21 l 3.5 13.3 100 33.9 46.0 20.1

V COMPARISON EXAMPLE 7 The same procedures as in Example 22 were repeated except that no water bath was used to supply steam to the disproportionation system. The results are indicated in Table 11.

Table 11 Dispro- Dispro- Content Composition of portionportionof isodisproportionation ation ation pentene product (/z) time converin C sion fraction C5 -Hl (hr) (7r) (7:) Propylene fraction fraction 5 .2 w... H .7. y. 2..

The product of disproportionation included a small amount of ethylene.

EXAMPLES 24 AND 25 AND COMPARISON EXAMPLE 8 In Examples 24 and 25, the same procedures as in Example 20 were repeated twice except that the disproportionation process was carried out at temperaturesof 300C (Example 24) and 350C (Example 25) in place of 250C, for 2.5 hours.

In Comparison Example 8, the same procedures as in Example 24 were carried out except that the disproportionation temperature was 200C.

The results are summarized in Table 12.

Table 12 Dispro- Dispro- Content Composition of portionportionof isodisproportionation ation ation pentene product (/z) Example temper converin C, C C No. ature sion fraction Profracfrac- (C) (7r) ('71) pylene tion tion Comparison 200 25.8 85.7 16.3 25.9 57.8 Example condition. The disproportionation process was carried out for 2.5 hours, in both Examples 26 and 27.

The results are indicated in Table 13.

The same procedures as in Example 20 were repeated twice except that the temperatures of the water baths to which the spent BB fraction gas to be disproportionated was introduced, were 25C (Example 28) and 60C (Example 29), and that after it was passed through the water baths, the spent BB fraction gas contained steam in amounts of 3.1% (Example 28) and 19.7% (Example 29) based on the volume of the spent BB fraction gas fed to the disproportionation process. The disproportionation process in both the examples was carried out for 2.5 hours.

The results are indicated in Table 14.

Table 14 Temper- Content Dispro- Content Composition of ature of of portionof isodisproportionation Ex. water steam ation pentene product bath converin C,, No. by sion frac- C, C (C) volume) tion Profracfracpylene tion tion EXAMPLES 30 THROUGH 37 The same operations as in Example 1 were repeated eight times except that a catalyst which has been'prepared in a similar manner'to that in Example 1, was composed of 86.5 parts by weight of alumina, 1 part by weight of the calcined tin compound calculated in terms of tin oxide (SnO), 3.5 parts by weight of the calcined cobalt compound calculated in terms of cobalt i oxide (C) and parts by weight of the calcined molybdenumcompound calculated in terms of molybdenum oxide (M00 and that the disproportionation processes were carried out, at the temperatures under the pressures indicated in Table 15.

The u t a e. isqisatsfialad l 5-,-

lyst contains 5 to 20% of said calcined molybdenum compound and 0.5 to 10% of said calcined additional metal compound based on the weight of said alumina carrier and calculated in terms of oxides corresponding thereto.

5. A method as claimed in claim 4, wherein the content of said calcined additional metal compound is l to 5% based on the weight of said alumina carrier and calculated in terms of the oxide corresponding thereto.

6. A method as claimed in claim 1, wherein said additional metal compound is selected from the group con sisting of halides, sulfates, nitrates, carbonates, hydroxides, oxides, hydroxycarbonates and organic acid salts of cobalt, tin, silver, zinc, cadmium, lead, bismuth and L .i3!19 Pl Table 15 Disproportionation Dispropor- Content of Composition of process tionation isopentene disproportionation product (3%) Example conversion in C,

No. Pressure Temperature fraction C C (kg/0mm) ("C Propylene fraction fraction What we claim is: 1. A method for the steps of:

bringing a hydrocarbon mixture containing isobutene and n-butene into contact, at a temperature of 220C to 380C, with a catalyst which has been prepared by depositing a molybdenum compound and at least one additional metal compound selected from the group consisting of cobalt, tin, silver, zinc, cadmium, lead, bismuth and antimony compounds on an alumina carrier and calcining the compounds deposited, thereon the contact being carried out in the presence of steam in an amount I of 0.1 to 25% based on the volume of said hydrocarbon mixture and calculated in terms of volume under standard conditions of a temperature of 0C and a pressure of 760 mmHg; isolating the resultant isopentene from the reaction mixture. 2. A method as claimed in claim 1, wherein said bydrocarbon mixture contains more than 30% by weight producing isopentene comprising j" -of isobute ne.

3. A method as claimed in claim 2, wherein said content of isobutene in said hydrocarbon mixture is between 30 and 60% by weight.

.A, h s a me n Claim 1. whets n' aid satamolybdenum chloride and molybdenum oxide chloride.

12. A method as claimed in claim 1, wherein said deposition of molybdenum compound and said additional metal compound on said alumina carrier is effected by an impregnation method.

13. A method as claimed in claim 1, wherein said calcining of said molybdenum compound and said additional metal compound deposited on said alumina carrier is effected at a temperature of 300 to l0O0C for 3 to 10 hours.

14. A method as claimed in claim 13, wherein said calcining temperature is 500 to 700C.

15. A method as claimed in claim 1, wherein said calcining is carried out in air.

7. A method as claimed in claim 1, wherein said alu- 16. A method as claimed in claim 1, wherein said hydrocarbon mixture is brought into contact with said catalyst at a flow rate of 50 to 2000 cm /hr, calculated in terms of volume under standard conditions, per 1 cm of said catalyst.

17. A method as claimed in claim 16, wherein said by volume of steam calculated in terms of volume under standard conditions, at a temperature of to 300C.

20. A method as claimed in claim 1, wherein the contact temperature of said hydrocarbon mixture with said catalyst is 230 to 350C. 4

21. A method as claimed in claim 1, wherein said isolation of said resultant isopentene is carried out by distillation at a temperature of 20 to 40C.

22. A method as claimed in claim 1, wherein said disproportionation step is carried out under normal pressure or under a pressurized condition up to 10 Kg/cm G. 

1. A METHOD FOR PRODUCING ISOPENTENE COMPRISING THE STEPS OF: BRINGING A HYDROCARBON MIXTURE CONTAINING ISOBUTENE AND N-BUTENE INTO CONTACT, AT A TEMPERATURE OF 220*C TO 380*C, WITH A CATALYST WHICH HAS BEEN PREPARED BY DEPOSITING A MOLYBDENUM COMPOUND AND AT LEAST ONE ADDITIONAL METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF COBALT, TIN, SILVER, ZINC, CADMIUM, LEAD, BISMUTH AND ANTIMONY COMPOUNDS ON AN ALUMINA CARRIER AND CALCINING THE COMPOUND DEPOSITED, THEREON THE CONTACT BEING CARRIED OUT IN THE PRESENCE OF STEAM IN AN AMOUNT OF 0.1 TO 25% BASED ON THE VOLUME OF SAID HYDROCARBON MIXTURE AND CALCULATED IN TERMS OF VOLUME UNDER STANDARD CONDITIONS OF A TEMPERATURE OF 0*C AND A PRESURE OF 760 MMHG, ISOLATING THE RESULTANT ISOPENTENE FROM THE REACTION MIXTURE.
 2. A method as claimed in claim 1, wherein said hydrocarbon mixture contains more than 30% by weight of isobutene.
 3. A method as claimed in claim 2, wherein said content of isobutene in said hydRocarbon mixture is between 30 and 60% by weight.
 4. A method as claimed in claim 1, wherein said catalyst contains 5 to 20% of said calcined molybdenum compound and 0.5 to 10% of said calcined additional metal compound based on the weight of said alumina carrier and calculated in terms of oxides corresponding thereto.
 5. A method as claimed in claim 4, wherein the content of said calcined additional metal compound is 1 to 5% based on the weight of said alumina carrier and calculated in terms of the oxide corresponding thereto.
 6. A method as claimed in claim 1, wherein said additional metal compound is selected from the group consisting of halides, sulfates, nitrates, carbonates, hydroxides, oxides, hydroxycarbonates and organic acid salts of cobalt, tin, silver, zinc, cadmium, lead, bismuth and antimony.
 7. A method as claimed in claim 1, wherein said alumina carrier has a 2 to 100 mesh size.
 8. A method as claimed in claim 7, wherein said mesh size of said alumina carrier is 5 to
 50. 9. A method as claimed in claim 1, wherein said alumina carrier consists of an activated alumina.
 10. A method as claimed in claim 9, wherein said activated alumina is either gamma -alumina or eta -alumina.
 11. A method as claimed in claim 1, wherein said molybdenum compound is selected from the group consisting of molybdenum oxide, ammonium molybdate, molybdenum chloride and molybdenum oxide chloride.
 12. A method as claimed in claim 1, wherein said deposition of molybdenum compound and said additional metal compound on said alumina carrier is effected by an impregnation method.
 13. A method as claimed in claim 1, wherein said calcining of said molybdenum compound and said additional metal compound deposited on said alumina carrier is effected at a temperature of 300* to 1000*C for 3 to 10 hours.
 14. A method as claimed in claim 13, wherein said calcining temperature is 500* to 700*C.
 15. A method as claimed in claim 1, wherein said calcining is carried out in air.
 16. A method as claimed in claim 1, wherein said hydrocarbon mixture is brought into contact with said catalyst at a flow rate of 50 to 2000 cm3/hr, calculated in terms of volume under standard conditions, per 1 cm3 of said catalyst.
 17. A method as claimed in claim 16, wherein said flow rate of said hydrocarbon mixture is 100 to 1000 cm3/cm3. catalyst/hr.
 18. A method as claimed in claim 1, wherein said steam is fed at a feed rate of 0.2 to 10% based on the volume of said hydrocarbon mixture and calculated in terms of volume under standard conditions.
 19. A method as claimed in claim 1, wherein said catalyst is treated with an inert gas containing 0.1 to 25% by volume of steam calculated in terms of volume under standard conditions, at a temperature of 100 to 300*C.
 20. A method as claimed in claim 1, wherein the contact temperature of said hydrocarbon mixture with said catalyst is 230* to 350*C.
 21. A method as claimed in claim 1, wherein said isolation of said resultant isopentene is carried out by distillation at a temperature of 20* to 40*C.
 22. A method as claimed in claim 1, wherein said disproportionation step is carried out under normal pressure or under a pressurized condition up to 10 Kg/cm2G. 